This invention relates to superconductive devices and, more particularly, to Josephson junction-type devices with semiconductor tunneling barriers.
Weak-link supercurrent devices take on a variety of configurations including point contact and restricted bridge structures as well as the more common thin film geometry. Devices in the latter class are generally formed by a thin tunneling barrier interposed between a pair of superconductors. This barrier may be a thin, normal metal layer in which case the device operation relies on the proximity effect, or, in more classic Josephson sense, may be a thin oxide layer, in which case operation is based on two-particle tunneling. More recently, some workers have succeeded in realizing experimental versions of Josephson junction-type devices in which the barrier is made of a semiconductor material such as single crystal Si [Huang and Van Duzer, APL, 25, 753 (1974)] or polycrystalline Sn/Ge [Hu and Jackel, U.S. Pat. No. 4,145,699 (1979)]. Hu et al used molecular beam deposition to grow the Sn/Ge barrier layer, the thickness and composition of which determine the capacitance and hysteresis of the junction. But, the polycrystalline nature of the barrier implies less reproducibility than a single crystal barrier, all other things being equal. In contrast, Huang et al etched wells into single crystal Si to produce precisely thinned membranes of heavily doped Si on which superconductor films are deposited. However, according to A. H. Silver et al [AIP Conference Proceedings, No. 44, page 364 (1978)], a principal problem with the latter technique is the alignment of two counter-electrodes on opposite sides of the membrane. In addition, it suffers from the fragility attendant the fabrication and handling of thin membranes.